This invention relates to the field of development of ligands for Ret and to the use of models of Ret binding site derived from crystal structures. The information provided is intended solely to assist the understanding of the reader. None of the information provided nor references cited is admitted to be prior art to the present invention. Each of the references cited herein is incorporated in its entirety.
The present invention relates to Ret protein and the development of modulators of Ret activity.
Ret (Rearranged during Transformation) was identified as a rearranged human oncogene in the classic NIH3T3 transformation assay (Takahashi et al., 1985, Cell 42(2):581-8) and subsequently characterized as a Receptor Tyrosine kinase (Takahashi et al., 1988, Oncogene 3(5):571-8).
Ret and NTRK1 are receptor tyrosine kinase (RTK) proteins which play a role in the development and maturation of specific components of the nervous system. Their alterations have been associated to several human diseases, including some forms of cancer and developmental abnormalities. These features have contributed to the concept that one gene can be responsible for more than one disease. Moreover, both genes encoding for the two RTKs show genetic alterations that belong to either “gain of function” or “loss of function” class of mutations. In fact, receptor rearrangements or point mutations convert Ret and NTRK1 into dominantly acting transforming genes leading to thyroid tumors, whereas inactivating mutations, associated with Hirschsprung's disease (HSCR) and congenital insensitivity to pain with anhidrosis (CIPA), impair Ret and NTRK1 functions, respectively.
Implication of Ret in human tumorigenesis was indicated by the frequent identification of rearranged Ret sequences that transformed NIH3T3 cells in the DNA isolated from Papillary Thyroid Carcinoma DNAs. Bongarzone et al., 1989, Oncogene 4(12):1457-62). In these cases, the Ret gene was fused to as yet unknown PTC DNA sequences in the tumor DNA but not the normal patient DNA (Grieco et al., 1990, Cell 60(4):557-63). In addition, the chromosomal mapping of Ret to chromosome 10q11.2 co-localized with genetic mapping data that implicated a gene involved in patients with MEN2A (Multiple Endocrine Neoplasia 2A) (Ishizaka et al. 1989 Oncogene 4(12):1519-21). Expression analysis of the RET oncogene in a number of human tumors consistently detected expression of normal-sized transcripts of the RET proto-oncogene in human pheochromocytomas and in human medullary thyroid carcinomas (MTC), both of familial and sporadic type (Santoro et al., 1990, Oncogene 5(10):1595-8).
Further analysis of the tumor DNA of patients with Multiple endocrine neoplasia type 2A (MEN 2A) and familial medullary thyroid carcinoma (FMTC) identified mutations in the RET sequence resulting in amino acid changes in the encoded Ret protein (Donis-Keller 1993, Hum Mol. Genet. 2(7):851-6). Likewise, mutations in the RET gene were correlated with Hirschprung disease, a developmental disorder with genetic deletions and mutations in the chromosomal location of the RET gene (Luo et al., 1993, Hum Mol. Genet. 2(11):1803-8).
By early 1994, multiple papers describe the inactivation of the RET gene in patients with Hirschsprung disease and similar phenotype in knock out mice. In addition, activating mutations in Ret are now identified in patients with MEN2A, MEN2B, and FMTC (reviewed by van Heyningen V., 1994, Nature 367(6461):319-20).
It was determined that c-Ret regulates cell survival. Signal transduction molecules that form a complex with c-Ret as a result of these phosphoryl moieties, such as GRB2, SOS, ras, and raf, propagate a signal in the cell that promotes neural survival. Thus, compounds that promote the interactions of the se stimulatory molecules of c-Ret would enhance the activity of c-Ret. Alternatively, protein phosphatases can remove the phosphoryl moieties placed on the intracellular region of c-Ret in response to GDNF, and thus inhibit the signaling capability c-Ret. Thus, compounds that inhibit phosphatases of c-Ret will probably enhance the signaling capacity of c-Ret.
C-Ret is implicated in the development and survival of enteric, synaptic, and sensory neurons and neurons of the renal system upon stimulation by GDNF (Jing, et al., 1996, Cell 85:1113-1124; Trupp, et al., 1996, Nature 381:785-789; Durbec, et al., 1996, Nature 381:789-793). Lack of function mutations in c-Ret can lead to Hirschsprung's disease, for example, which manifests itself as a decrease in intestinal tract innervation in mammals. Thus, compounds that activate c-Ret are potential therapeutic agents for the treatment of neurodegenerative disorders, including, but not limited to, Hirschsprung's disease, Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis. Compounds that inhibit c-Ret function can also be anti-cancer agents as over-expression of c-Ret in cells is implicated in cancers, such as cancer of the thyroid.
Modulation of c-Ret activity may also be useful in treating cancers of the nerve tissue, such as neuroblastoma, even if an abnormality is not found the signaling pathway.
As stated above, RET gene is responsible for MEN2 syndromes, which are inherited in an autosomal dominant fashion with high penetrance and diverse clinical manifestations. The predominant RET mutation is missense mutation which is restricted to 9 codons (codons 609, 611, 618, 620, 630, 634, 768, 804 and 918). The MEN2 syndromes have 3 subtypes: multiple endocrine neoplasia type 2A (MEN2A), MEN2B, and familial medullary thyroid carcinoma (FMTC). Missense mutations at exon 10 (codons 609, 611, 618, and 620) and exon 11 (codons 630 and 634) have been identified in 98% of MEN2A families and in 85% of FMTC families. Missense mutations at codons 768 and 804 have been known to be responsible for 5.about.10% of FMTC cases. In addition, missense mutations at exon 16 (codon 918) have been found in 95% of MEN2B cases.